Nowadays, in addition to improving basic performance and safety, automobiles are required to improve convenience. In order to satisfy such demands, an engine drive control system has been proposed in which automatic wireless communication is performed between a portable device carried by a user and an in-vehicle vehicle control device, and the starting of the engine is enabled when wireless communication is established (refer to, for example, patent document 1 and patent document 2).
In a conventional engine drive control system, the vehicle control device intermittently outputs a request signal through wireless communication. A transmittable range of the request signal is set to be within the passenger compartment. When a user (driver) carrying the portable device, which has a communication function, enters the passenger compartment, the portable device receives the request signal. In response to the request signal, the portable device wirelessly outputs an ID code signal containing an ID code that is set or registered in the portable device. The vehicle control device receives the ID code signal and authenticates the ID code contained in the ID code signal of the portable device with an ID code set or registered in the vehicle control device. The vehicle control device determines that communication has been established when the ID codes are identical and enables the engine to be started. In this state, the engine is started by operating an operation unit arranged in the passenger compartment. A driver can start the engine by just entering the vehicle and operating the operation unit.
In the conventional engine drive control system, however, the passenger compartment may include a region in which communication between the portable device and the vehicle control device is impossible. When the portable device enters such a non-communicable region, the user cannot start the engine even through the portable device is located in the passenger compartment. This is inconvenient. Accordingly, improvements have been made so that the request signal can be transmitted throughout the passenger compartment by arranging a plurality of transmission antennas that output the request signal in the passenger compartment or by adjusting the directivity of a transmission antenna.
The request signal output throughout the passenger compartment from the transmission antennas, the quantity and directivity of which have been adjusted, is blocked by the door when the door is closed and is not transmitted outside the vehicle. However, when the door is open, the request signal may be transmitted out of the vehicle. When the user is carrying the portable device near the open door, mutual communication may be established between the portable device and the vehicle control device even though the user is outside the vehicle such that starting of the engine is enabled. In the state in which starting of the engine is enabled, a third person may start the engine against the will of the user when, for example, the user is loading baggage at the rear of the vehicle in a state in which a back door is open. Improvements in security must thus be made in the conventional engine drive control system.
Patent document 2 discloses a technique for changing the transmission region of the request signal in the passenger compartment when the rearmost seat is in a stored state and an upright state to prevent the request signal from being transmitted out of the vehicle. The security is improved by keeping the rearmost seat in the stored state.    [Patent document 1] Japanese Laid-Open Patent Publication No. 2001-311333    [Patent document 2] Japanese Laid-Open Patent Publication No. 2005-105691